1. Field of the Invention
This invention relates to a method and assembly for producing extruded permanent magnet articles from particle charges of permanent magnet alloys.
2. Description of the Prior Art
It is known to produce permanent magnet articles by powder metallurgy techniques, which include the consolidation of particles of the permanent magnet alloys. These practices are employed with permanent magnet alloys of at least one rare earth element and transistion element. These conventional practices generally include the steps of aligning, pressing and sintering. With prior art practices of this type, high energy product (BH.sub.max) and uniaxial anisotropic crystal alignment is achieved, and this combination finds utility in various permanent magnet applications.
Uniaxial anisotropic crystal alignment, however, is not always advantageous for magnet applications for rotating machinery, motor rotors, beam focusing devices and the like. For these applications a [100] fiber texture wherein the C crystallographic axis is perpendicular to the axis of the magnet may be desired. One of the primary applications for magnets of this construction is for use in DC motors. In this application, with conventional practice, multiple segments of uniaxial anistropic magnets are needed to form the armature for the motor, which segments are identified as 2 positioned around a motor shaft 4 in FIG. 1.
To obviate the need for the use of a plurality of magnet segments, as shown in FIG. 1, it is known to extrude a cylindrical magnet conforming to the required dimensions of the motor shaft. An extruded magnet 6 in association with a motor shaft 4 is shown in FIG. 2.
Cylindrical, extruded magnets, as shown in FIG. 2, are conventionally produced by the use of a cylindrical extrusion container. Magnet alloy particles are introduced to the container, and the container is outgassed, evacuated and sealed. Thereafter, the container is heated to extrusion temperature and extruded to consolidate the particles to substantially full density. The hollow center of the magnet is achieved by the use of a solid cylinder or mandrel of a diameter corresponding to the internal diameter of the magnet to be produced, which cylinder is attached to the extrusion ram. This solid cylinder moves with the extrusion ram during the extrusion operation and thereby maintains the desired inner diameter of the extruded magnet. It is difficult to maintain concentricity of the inner and outer peripheries of the extruded magnet because the mandrel tends to wander and thus is not maintained in axial alignment during the extrusion operation. In addition, at the high extrusion ratios breaking of the mandrel may occur. It may be seen, therefore, that in producing cylindrical magnets by conventional extrusion practices, a cylindrical magnet having the required concentric dimensions is difficult to achieve.